Extent of indigenous vegetation on land
Why we monitor the extent of indigenous vegetation
Areas of indigenous vegetation are an important storehouse of indigenous biodiversity. New Zealand is known internationally for its unusual plants and animals, many of which are found nowhere else in the world.
Loss of habitat, along with the introduction of animal and plant pests, has had a major role in extinctions and the high number of threatened species in New Zealand.
In the Waikato region, approximately 22 endemic species have become extinct, and more than 220 indigenous species are known to be threatened
Some ecosystem types, for example lowland forest and coastal forest, scrub and shrubland, have become very rare because the land they grew on is highly valuable for other uses such as farming or urban settlement.
Change in extent of native vegetation means potential change in the diversity and security of native species.
Indigenous vegetation extent and distribution change indicates where natural areas have:
- reduced - for example through clearance
- increased - for example on retired land or part of restoration efforts
- changed - for example scrub and shrubland have developed into native forest.
Waikato Regional Council monitors changes in vegetation extent to provide information on where land use pressures are occurring, which vegetation and habitat types are at greatest risk of loss and for reporting on biodiversity. This helps us identify policy responses to avoid or reverse adverse affects on our biodiversity.
This indicator is restricted to terrestrial indigenous forest, scrub and shrubland and tussock grassland.
Before European settlement (around 1840) the only land in the Waikato region not covered by indigenous (native) vegetation was areas of bare rock or permanent snow and ice. Forest covered 52 per cent of the region, but scrub and shrubland and tussock grassland grew where fires were frequent, or the land too wet or cool for forest.
Change in land use, for example to agriculture, plantation forestry and urban settlement, has required clearing indigenous vegetation. Today, 27 per cent of the region’s land area is in indigenous vegetation cover. The remaining extent of indigenous forest, scrub and shrublandand tussock grassland combined is around 649,458 ha. Other natural areas in the region include wetlands and coastal habitats which are reported in separate indicator report cards.
The greatest loss of indigenous terrestrial (land-based) vegetation since 1840 occurred in the central Waikato lowlands, around Hamilton City and in the Waipa, Waikato, South Waikato and Matamata-Piako districts where fertile soils on gentler topography were suitable for livestock farming, or where the hills were cleared for pine plantations. Districts with more rugged hill country and extensive ranges, such as Taupo, Otorohanga, Waitomo and Thames-Coromandel have a greater proportion of indigenous forest, scrub and shrubland and tussock remaining.
Coastal, lowland and sub-montane bioclimatic zones (below 800 metres elevation) lost the greatest portion of their indigenous cover, with over 60 per cent of each of these zones cleared for another land use.
In more recent times, the rate of indigenous vegetation loss in the region has slowed, as much of the productive land has already been cleared and 70 per cent of remaining indigenous forest set aside in reserves.
Between 1996 and 2012, the Land Cover Database (LCDB) records an estimated net loss of 487 ha of indigenous forest and 648 ha of indigenous scrub and shrubland (on average just over 71 ha net loss per year). The actual loss of indigenous forest over this time period is likely to be less than 487 ha, because some areas of scrub and shrubland or plantation forest were misclassified as indigenous forest in the 1996 LCDB version. More detailed air photo analysis confirms that over 50 ha of indigenous forest has been cleared since 1996, including one 42 ha patch that was felled and converted to pasture.
The actual amount of scrub and shrubland cleared or lost through natural causes, such as fire or landslide, was over 5000 ha, but offset by establishment of over 4000 ha of new scrub and shrubland, most likely the result of natural regeneration on retired land, along with community and agency restoration planting. Areas formerly classified as scrub and shrubland are now either pasture (46 per cent) or plantation forestry (50 per cent).
Most of the recent loss of indigenous vegetation has been from the lowland bioclimatic zone. There was no measurable change in area of tussock grassland, or of any vegetation types in the areas above 800 meters elevation (montane to alpine zones). The loss of over 1000 ha of scrub and shrubland from the lowland areas was partly offset by gains in the coastal and submontane zones.
While there was no apparent increase in the amount of indigenous forest in any of the bioclimatic zones, over time it is likely to increase through natural maturation (succession) of areas of scrub and shrubland into forest. The region is likely to see an ongoing decrease in the extent of scrub and shrubland vegetation over the coming decades because of the:
- higher rate of clearance of scrub and shrubland compared with other native vegetation
- lower proportion of scrub and shrubland in protected areas
- natural maturation process of scrub and shrubland into forest.
However, restoration planting and retirement of unproductive land may offset this to some extent.
Most of the indigenous forest, scrub and shrubland that have been lost were from the districts with the largest proportion of their pre-European vegetation remaining (Otorohanga, Taupo, and Thames-Coromandel), along with Hauraki and Waikato districts. Each lost between 50 and 130 ha of indigenous forest, however, Otorohanga also experienced an increase in the amount of scrub and shrubland.
When this indicator is updated
The updating of this indicator is dependent on production of the updated LCDB. Because of the time scale at which vegetation change (other than clearance/drainage) occurs, it is unlikely that change will be monitored any more frequently than five yearly.
Contact at Waikato Regional Council
Terrestrial Ecologist - Science and Strategy Directorate.